The present invention relates to the evaluation of male sexual dysfunction and, in particular, it concerns a method and device for evaluating the occurrence of nocturnal penile erection in a male suffering from impotence.
Impotence, or male erectile dysfunction (ED), is defined as the inability to achieve or maintain an erection adequate for the performance of sexual intercourse. Erectile dysfunction impairs sexual performance, diminishes self-(esteem and disrupts personal relationships. It affects approximately 10-20 million men in the US according to the NIH Consensus Development Panel on impotence (JAMA 1993,270:83-90).
For a penile erection to be adequate for the performance of sexual intercourse it is necessary that the erect penis be both adequately tumescent (that is, enlarged and swollen relative to it's flaccid state) and adequately rigid. The process of penile erection occurs in several phases:
1. During the initial , flaccid, phase the volume of the penile erectile tissue (the corpus cavenosum) is small (approximately 20% of maximum volume) and the corporal al pressure is low (approximately 20 mmHg). PA0 2. During the tumescent, or filling, phase a reduction in alpha-sympathetic tone results in dilation of the penile arteries and constriction of the penile veins, thus allowing arterial blood to build up in the corpus cavenosum. This causes the corporeal pressure to rise, pressing the penile veins against the surrounding tunica and further increasing the hemodynamic resistance to venous outflow. As the intra-corporeal pressure approaches systolic levels (100 mmHg), the volume of the penile erectile tissue grows by approximately 80%. PA0 3. During the rigid phase, contraction of the perineal muscles and the pressure of the corpus cavernosum against the taut surrounding fibrous coats result in the rigidity required for full erection. PA0 4. The phase of detumescence begins with contraction of the penile arteries, thus restricting arterial inflow, and reopening of venous drainage from the erectile tissue. This causes corporal volume and pressure to gradually return to flaccid levels.
Tumescence is thus controlled by the autonomic nervous system, which regulates blood flow to the penis, while rigidity is related to the pressure-volume relationship of the tumescent erectile tissue and it's surrounding fibrous fascia, and is also influenced by local muscle tone. As tumescence that is not followed by sufficient rigidity does not result in a functional erection, both these phase of penile erection should be evaluated when assessing male sexual dysfunction. Tumescence monitoring alone, therefore, without a concomitant assessment of penile rigidity, allows for only a limited description of erectile function (Levine LA and Lenting EL,. Use of Nocturnal penile tumescence and rigidity in the evaluation of male erectile dysfunction. Urol Clin North Am 1995 Nov;22(4):775-788).
During sleep, normal fluctuations in autonomic neural tone result in periodic, transient penile erections. When erectile dysfunction is of psychological origin, these nocturnal erections are unaffected. However, when dysfunction is organic in nature, an absence of nocturnal penile tumescence and rigidity (NPTR) can be expected. Thus, to assess whether male sexual dysfunction due to inadequate penile tumescence and/or rigidity is organic or psychogenic in origin, it is necessary to monitor the patient for the occurrence of penile tumescence and rigidity during sleep.
Several methods and devices for measuring nocturnal tumescence have been described. Thus, strain gauges installed on elastic bands (U.S. Pat. No. 4,572,211 and U.S. Pat. No. 4,700,715), or on silicon rings filled with mercury (U.S. Pat. No. 4,103,678 to Karacan) have been used to passively measure nocturnal changes in penile circumference (indicating the occurrence of tumescence). These devices suffer from the deficiency that they provide no measurement of penile rigidity. Furthermore, the mercury within the device of Karacan is a hazardous substance, which may induce toxic effects if it leaks from the silicon ring and comes into contact with the patient's skin.
A device for passively measuring penile rigidity (the occurrence of which implies that tumescence must have occurred as well) has been described by Timm in U.S. Pat. Nos. 4,474,187, 4,766,909, and 4,911,176. In this device, a wire surrounding the penis snaps at a predetermined force, thus indicating that penile rigidity has surpassed a predetermined level. This device suffers from the deficiency that the measurement of rigidity is not quantitative, thus precluding an assessment the number and timing of episodes of erection during the course of a nocturnal study. Goldstein (U.S. Pat. No. 4,469,108) described a mechanical, manually operated device for measuring penile rigidity. This device is thus unable to automatically monitor rigidity during sleep.
Timm (U.S. Pat. Nos. 4,515,166 and 4,848,361) described a device capable of actively measuring both tumescence and rigidity (the "Rigiscan", Dacomed Corporation, Minnesota, USA). This device utilizes electrical torque motors to apply tension to a wire ending in a loop placed on the penis. The motor applies an intermittent force, every 15 to 30 seconds, to the wire, which forms a slipknot loop around the penis. Shortening of the wire loop is measured with each application of torque. When the penis is fully rigid and unyielding, the wire will not shorten at all, while lesser degrees of rigidity will result in variable degrees of shortening of the wire.
Although this device allows for the automatic measurement of both tumescence (indicated by a progressively enlarging wire loop) and rigidity (indicated by progressively lesser degrees of wire shortening in response to torque), the Rigiscan suffers from the deficiency that it measures these parameters by active means, that is, force or pressure on the penis is actively generated so as to measure the compliance of the penile tissue. This procedure is uncomfortable and disturbing for the patient. Furthermore, the force generating elements (two torque motors) are large and unwieldy, making such devices cumbersome for the patient to wear while sleeping (measuring approximately 21 cm by 5 cm and weighing over 1.5 Kg). Indeed, the Rigiscan causes such discomfort when attached to the patients thigh that it is necessary to attach the device to the patient on two consecutive nights prior to performing the study, so as to accustom the user to sleeping with a heavy device attached to his thigh.
Lavoisier described a device for actively measuring rigidity by measuring the water pressure in a rigid cuff surrounding the penis (U.S. Pat. Nos. 4,747,415, and 5,692,520). Trick (U.S. Pat. No. 4,928,706) described a device in which the flow of water from one cuff surrounding the penis into a second, connected cuff is used to quantify the degree of tumescence, and displacement of an active sensor in the second cuff is used to determine rigidity. Both these devices utilize fluid filled cuffs placed around the penis and achieve their measurements by active means. They thus suffer from the same deficiencies as described above for the Rigiscan.
There is therefore a need for, and it would be highly advantageous to have, a single device capable of automatically measuring both penile tumescence and penile rigidity by passive means. Such a device should be sufficiently small and lightweight as to be comfortable for the user to wear, and thus not disturb the users sleep. Furthermore, the passive means used to measure penile tumescence and rigidity should not cause pain or discomfort to the user, and the device should be safe to wear, with no risk of exposure to noxious substances involved.